The present invention relates to an aqueous alkaline solution for use in recovering oil from a reservoir which contains significant quantities of clay in the calcium and magnesium form and significant proportions of water soluble calcium and magnesium salts. More particularly, the invention relates to a process of tailoring the alkalinity of such an alkaline solution to enhance the performance of surfactant materials by suppressing their exposure to calcium and magnesium ions.
Numerous processes have been proposed for recovering oil by displacing it with aqueous alkaline solutions. For example, such processes are described in the following patents: U.S. Pat. No. 3,771,817 describes injecting an aqueous alkaline solution for satisfying surfactant adsorption sites on a reservoir rock and then injecting a surfactant containing aqueous liquid that may also contain alkali. U.S. Pat. Nos. 3,804,170, 3,804,171 and 3,847,823 describe injecting aqueous alkaline solutions containing overbased petroleum sulfonate surfactants formed by overneutralizing petroleum hydrocarbon sulfonates. U.S. Pat. No. 3,927,716 describes injecting an aqueous alkaline solution to neutralize the organic acids in the oil and form surfactants in situ with the solution having a specified pH and concentration of neutral monovalent salt. U.S. Pat. Nos. 3,997,470 and 4,004,638 describe first injecting an aqueous alkaline solution and then an alkaline solution containing a preformed surfactant. U.S. Pat. No. 4,468,892 describes alkaline flood using water such as seawater which contains multivalent ions that have been stabilized by adding a lignosulfonate before adding the alkali.
Alkaline floods have been conducted by many different companies over the years in attempts to recover more oil than could be recovered by simple water flooding. Alkaline materials such as sodium hydroxide, sodium orthosilicate, sodium carbonate and ammonia have been used in such waterfloods. But, as far as Applicants are aware, the alkaline materials have been used individually, although mentions such that "use could be made of substantially any" of a list of materials "and/or mixtures thereof" may be found in patents. In addition, in at least some sense, any such use of an aqueous, e.g., sodium orthosilicate involves using a mixture of a sodium silicate and sodium hydroxide. And, it appears that no one has previously discovered a benefit which can be provided by an aqueous alkali containing a reservoir-tailored mixture of alkali metal carbonates and silicates.